The present application relates to a composition usable for preventing or treating Streptococcus parauberis infections comprising an isolated bacteriophage that is able to infect and kill Streptococcus parauberis cells, and a method for preventing and treating Streptococcus parauberis infections using the composition. More particularly, the present application relates to the bacteriophage characteristically having the genome represented by nucleotide sequence of SEQ. ID. NO: 1 that is able to kill specifically Streptococcus parauberis cells, a composition comprising the bacteriophage for preventing and treating Streptococcus parauberis infections and a method for preventing and treating Streptococcus parauberis infections using the composition.
The importance of aquaculture production in the fishery industry increases continuously. Because the wild fish captured are not sufficient to meet global fish demand, the supply and demand of aquaculture products are expected to increase continuously. Aquaculture production is expected to remain an important part of fishery industry.
In aquaculture production, disease outbreaks are considered to be a key constraint in the fish farming sector, resulting in significant losses. Disease outbreaks cause the economic damage and reduced productivity attributed to the increased general expense of fish culture resulted from the increase of drug use and management costs thereby. In addition, antibiotics residue has been another sensitive social issue, so the production of high quality safe aquatic products seems to be in doubt. Therefore, a method for preventing and treating the disease of cultured fish has been a major interest not just domestically, but internationally.
Streptococcus parauberis is well known as one of the most representative causative pathogen of streptococcosis in cultured fish. In addition to Streptococcus parauberis, S. iniae, S. difficilis, S. shiloi, and Lactococcus garvieae are also known as pathogenic bacteria that cause streptococcosis. Among them, Streptococcus parauberis is the most frequently reported causative pathogen of streptococcosis in fish.
In terms of external signs, a sea fish having streptococcosis shows darkened body color, exophthalmos and hyperemia, abdominal distension, and hernia. Internally, such symptoms as ascites, abdominal wall hemorrhage, and heart abscess were observed. In some cases, only gill erosion is observed without any other symptoms. Streptococcosis usually occurs in adult fish rather than a juvenile fish, indicating that economic damage is comparatively higher than other bacterial diseases.
Outbreak of streptococcosis can be influenced by several factors of deterioration of environmental conditions, inappropriate culture methods, and inappropriate feeds, etc. Streptococcosis is commonly found when water temperatures are warm, but may be common in the winter when water temperatures are low. The damage in the aquaculture production by such Streptococcus parauberis infections is getting bigger, so that a method to prevent the infections and also to treat the infections efficiently is urgently requested.
A variety of antibiotics have been used for the prevention or treatment of Streptococcus parauberis infections. However, according to the increase of antibiotic-resistant bacteria, another way of treating the infections is urgently requested. To control the infections caused by Streptococcus parauberis, a vaccine has been developed. However, the variety of vaccines cannot catch up with the variety of diseases. In addition, to control the multiple diseases broken at the same time, a combined control method to treat them along with a vaccine has to be prepared.
Recently, the use of bacteriophages has drawn our attention as a new way of treating bacterial infections. Particularly, the reason of our high interest in bacteriophages is because bacteriophage-based treatment is a nature-friendly method. Bacteriophages are an extremely small microorganism that infects bacteria, which is called phage in short. Once it infects bacteria, the bacteriophage is proliferated in the inside of the bacterial cell. After full proliferation, the progenies destroy the bacterial cell wall to escape from the host, suggesting that the bacteriophage has bacteria killing ability. The bacteriophage infection is characterized by high specificity, so that a certain bacteriophage infects only a specific bacterium. That is, the bacterium that can be infected by certain bacteriophage is limited, suggesting that bacteriophage can kill only a specific bacterium and cannot harm other bacteria.
Bacteriophage was first found out by an English bacteriologist Twort in 1915 when he noticed that Micrococcus colonies melted and became transparent by something unknown. In 1917, a French bacteriologist d′Herelle found out that Shigella disentriae in the filtrate of dysentery patient feces melted by something, and further studied about this phenomenon. As a result, he identified bacteriophage independently, and named it as bacteriophage which means a bacteria killer. Since then, bacteriophages specifically acting against such pathogenic bacteria as Shigella, Salmonella typhi, and Vibrio cholerae have been continuously identified.
Owing to the unique capability of bacteriophage to kill bacteria, bacteriophages have been studied and anticipated as a method to treat bacterial infections. However, after penicillin was found by Fleming, studies on bacteriophages had been only continued in some of Eastern European countries and the former Soviet Union because of the universalization of antibiotics. After the year of 2000, the merit of the conventional antibiotics faded because of the increase of antibiotic-resistant bacteria. So, bacteriophages are once again spotlighted as a new anti-bacterial agent that can replace the conventional antibiotics.
According to the recent regulation of use of antibiotics by the government, the interest on bacteriophages increases more and more.
Thus, the present inventors tried to develop a composition for preventing or treating Streptococcus parauberis infections by using an isolated bacteriophage that is able to kill Streptococcus parauberis cells specifically and to establish a method for preventing or treating Streptococcus parauberis infections using the composition. As a result, the present inventors secured the nucleotide sequence of the genome that can distinguish this bacteriophage from other bacteriophages and then developed a composition comprising the isolated bacteriophage as an active ingredient, and further confirmed that this composition could be efficiently used for the prevention and treatment of Streptococcus parauberis infections.